The present invention relates generally to the functional electrical stimulation (FES) arts. More particularly, the present invention relates to a method and apparatus for sensing hypoglossal nerve activity in human patients to detect obstructive sleep apnea, and using the sensed hypoglossal nerve activity to trigger selective functional electrical stimulation of the hypoglossal nerve, itself, for purposes of improving upper airway patency and, thus, treating obstructive sleep apnea. Further, the present invention relates to an improved hypoglossal nerve stimulation electrode interface that allows for simultaneous hypoglossal nerve activity sensing and nerve stimulation by eliminating stimulation artifacts that would otherwise trigger further, erroneous stimulation.
Obstructive sleep apnea (OSA) is the recurrent occlusion of the upper airways of human patients during sleep. In these patients, the upper airways obstruct as often as several times a minute with each episode lasting as long as 20-30 seconds. Each apneic episode ends with a brief arousal from sleep. Consequently, arterial oxyhemoglobin saturation decreases drastically. Complications include excessive daytime sleepiness, restless sleep, morning headache, job-related accidents, impaired short-term memory, polycythema, hypertension, right-sided congestive heart failure, decreased libido, and the like. Personality disorder and other psychological problems may also develop over time. Obstructive sleep apnea is found in 2 to 4 percent of the population, primarily in adult men and post-menopausal women.
In humans, the hypoglossal nerve innervates the intrinsic and extrinsic muscles of the tongue and the geniohyoid muscle. Of these muscles innervated by the hypoglossal nerve, the genioglossus and the geniohyoid muscles are the primary muscles involved in dilating the upper airways (UAWS) . Contraction of the genioglossus muscle provides tongue protrusion and, hence, dilates the airways.
It is generally known that the flow of inspired air is doubled by stimulation of the main branch of the hypoglossal nerve. Stimulation of the medial branch was nearly as effective and was superior to stimulation of other branches. Attempts have been made to improve upper airway patency in humans during sleep via direct electrical stimulation of the hypoglossal nerve. Further, various physiological variables have been used to synchronize the electrical stimulation with respiration. Hypopharyngeal or espophageal pressure measurements, airflow measurements made with thermistors placed near the nose and mouth, and tracheal inter-ring distance measurements made with a strain gauge are examples of physiological variables that have been investigated for use in synchronization of electrical stimulation of the hypoglossal nerve and/or the genioglossus muscle. However, all of these methods have drawbacks and limitations.
Other treatment methods for obstructive sleep apnea have included use of a nose mask through which continuous positive airway pressure is applied to keep the upper airways open. This therapy must be continued indefinitely, and only 60-65 percent of these patients can tolerate the technique long-term. Tracheostomy is another treatment for severe obstructive sleep apnea, but it is rarely used because of low patient acceptability and relatively high morbidity. Uvulopalatopharyngoplasty, removal of redundant tissue in the oropharynx, and other surgical operations to correct anatomical abnormalities in the upper airways can be considered in certain cases. However, in general, all of the above-mentioned therapies are associated with complications and disadvantages. Weight loss may improve the condition in mild cases, but pharmacologic attempts to treat obstructive sleep apnea by increasing pharyngeal muscle activity during sleep have not been found to be effective. Presently, electrical stimulation of the tongue muscles is the only known alternative treatment method that may provide some benefits.
In light of the foregoing, there has been found a need for a fully implantable functional electrical stimulator apparatus and method for treatment of obstructive sleep apnea that provides for both reliable detection of airway occlusion and that relieves same by selective electrical stimulation of the hypoglossal nerve. Further, a need has been identified for such a method and apparatus that accomplishes these results without relying upon use of external (i.e., non-implanted) devices that require percutaneous and/or transcutaneous interfaces and without requiring use of multiple, separate electrodes and sensors. Also, it has been deemed necessary to provide a method and apparatus for simultaneously sensing hypoglossal nerve activity and for using the sensed hypoglossal nerve activity to trigger selective electrical stimulation of the hypoglossal nerve without erroneously triggering further stimulation due to stimulation artifacts.
In accordance with the present invention, a new method and apparatus are provided for treating obstructive sleep apnea in humans by way of closed-loop electrical stimulation of the hypoglossal nerve, wherein activity of the hypoglossal nerve, itself, triggers the electrical stimulation.
In accordance with a first aspect of the present invention, a method of treating obstructive sleep apnea in a human patient comprises monitoring the patient for occlusion of his/her upper airways associated with obstructive sleep apnea by sensing electroneurogram activity of the patient""s hypoglossal nerve. The hypoglossal nerve of the patient is directly electrically stimulated when occlusion of the upper airways occurs as indicated by the sensed electroneurogram activity of the hypoglossal nerve.
In accordance with a more limited aspect of the invention, the electroneurogram signal of the patient""s hypoglossal nerve, itself, is used to trigger the direct electrical stimulation of the hypoglossal nerve.
In accordance with another aspect of the present invention, an apparatus for treatment of obstructive sleep apnea comprises means for detecting at least partial occlusion of upper airways of a human patient by sensing electroneurogram activity of a hypoglossal nerve of the patient. Means are provided for directly electrically stimulating the hypoglossal nerve of the patient in response to at least partial occlusion of the upper airways of the patient as indicated by the detecting means.
In accordance with still another aspect of the present invention, an apparatus adapted for simultaneously electrically stimulating body tissue and monitoring electrical activity of the body tissue being electrically stimulated without stimulation artifact is defined. The apparatus includes an electrical stimulation source and a sensor in contact with body tissue. A first stimulation contact is also in contact with the body tissue, and the said body tissue defines an electrical path between the first stimulation contact and the sensor having a first electrical impedance. A second stimulation contact is also in contact with the body tissue, and the body tissue defines an electrical path between the second stimulation contact and the sensor that has a second electrical impedance. The first impedance is substantially equal to the second impedance. A trigger receives input from the sensor and selectively triggers electrical stimulation of the body tissue by the stimulation source so that at least one electrical pulse passes between the first and second stimulation contacts through the body tissue. During stimulation, the potential difference established between the first stimulation contact and the sensor in response to the electrical pulse is substantially equal in magnitude to the potential difference established between the second stimulation contact and the sensor.
One advantage of the present invention resides in the provision of a method and apparatus for closed-loop stimulation of the hypoglossal nerve in a human to treat obstructive sleep apnea.
Another advantage of the present invention is found in the provision of a method and apparatus for treatment of obstructive sleep apnea wherein hypoglossal nerve activity is sensed and used to determine when upper airway occlusion associated with obstructive sleep apnea is occurring.
Still another advantage of the present invention is the provision of a method and apparatus for stimulation of the hypoglossal nerve in obstructive sleep apnea patients wherein sensed activity of the hypoglossal nerve in the patient triggers electrical stimulation of the hypoglossal nerve when the sensed activity of the hypoglossal nerve is indicative of occlusion of the patient""s upper airways so that the occlusion is prevented or removed.
A further advantage of the present invention is the provision of a method and apparatus for closed-loop stimulation of the hypoglossal nerve in obstructive sleep apnea patients wherein hypoglossal nerve activity is sensed simultaneously with stimulation of the hypoglossal nerve.
Still another advantage of the present invention resides in the provision of an apparatus for treatment of obstructive sleep apnea in human patients wherein the apparatus is totally implantable in the patient and requires no external devices or percutaneous electrical leads.
A yet further advantage of the present invention is found in the provision of a method and apparatus for closed-loop stimulation of the hypoglossal nerve in human patients for purposes of treating obstructive sleep apnea wherein a single, multiple-contact (i.e.,  greater than 1 contact) electrode is implanted in the patient for sensing/stimulation rather than multiple, separate electrodes/sensors.
A still further advantage of the present invention resides in the provision of a method and apparatus for treatment of obstructive sleep apnea wherein the onset of obstructive sleep apnea is predicted so that it can be prevented before it becomes severe.
Still other benefits and advantages of the present invention will become apparent to those of ordinary skill in the art to which the invention pertains upon reading and understanding the specification and accompanying drawings.